Playstation 3 ofcourse. Why? because the I have a Playstation 3
about 3 ft away from my current location, a Xbox 360 and a wii next to it, and i can easily say that the PS3 wins hands down. The playstation 3 is the most powerful out of the two, and yet makes far less fan noise. This power isn't just on paper, but is being expressed through fine detail in a games visuals, fast frame rate in games (resulting in smoother gameplay motion), Full 1080p HD visuals (i dont have a 1080p tv, but i can easily say that the visuals still blow me away on my SD tv!). Also, because the PS3 has a Blu-ray drive, and the games are on Blu-ray disks, developer now have 50GB worth of space o put their games on, which mean longer games with better graphics, gameplay and features than the 360's games (which are on DVDs - allowing developers to work with a mere 8.5GB - resulting in less features - for example: graphics will be worse than blu-ray games). The 360 on the other hand is noisy, has a worse interface and the online store is a shambles compared to the PS store, and the visuals of the PS3 are 2nd rate compared to the PS3. You may think that you will be able to tolerate the 360s noise level, but trust me, unless your gonna wear ear plugs while you use it, it will definately irritate the hell outta u. Because of this fan noise, using the 360 as a media centre/DVD player is almost unbearable - and crankin your volume up wont work either, cz when watchin videos, there's bound to quiet moments in the audio. Also, the games on the PS3 are WAY more fun than the games on the 360. The PS3 is so far more reliable than the 360 aswell; the PS3's cell processor is designed to run 24/7 without malfunctioning, wheras my 360 runs for about 4 hours before it crashes, and i have 2 wait 1/2 an hour for it to cool down again (I have so far only left the PS3 running for 16 hours, and no issues whatsoever. Also, i have had to have 2 replacement 360's due to the infamous 'ring of death' (look it up on google), where the 360 dies caused by a poor design.
The online or both systems is pretty much similar, however, the PS3's is much easier to navigate and has all the features the Live has. Purchasing content is easier on the PS3 because the currency used in the online store is in £ (for UK anyway), instead of shi.tty points: which is what the 360 uses.
Memory on the PS3 is much better because you can replace the Hard drive with any 2.5" SATA laptop drive (i'm planning on getting a 200GB one soon), which is far superior to Microsoft's compulsory 120GB drive, which cannot be replaced with a Hard Drive that is not by Microsoft, which means that 120GB is your limit if you choose the 360, whereas you will be able to buy bigger and BIGGER hard drives for the PS3 as they are manufactured (by any company).
Also, sony sends you a free blu-ray copy of Casino Royal as a way of saying thanks, ounce you sign up for a FREE PSN account (FREE is in caps to highlight the fact that you are getting a sevice that is far more superior to Xbox Live (of which, you must pay a fee of £35 per ear!) )
Anyway, while your making your mind up, i'll be watching a few blu-ray movies on my extremely quiet PS3.